From nobody Sun Dec 14 12:12:45 2025 Received: from mailtransmit04.runbox.com (mailtransmit04.runbox.com [185.226.149.37]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C13A530BF6E for ; Fri, 12 Dec 2025 19:38:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.226.149.37 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765568299; cv=none; b=mqTsxjAt2tnbbBkx5yTNzrMEzkFqGjVvTsYcBy3DRWFhxVqvzeEiAm0XBAjNZfk2UUKMoAbdQTQxIP9fyOOfb6MmsncwZhRXc23kUT1zOhS/nr/be0rrIAeFSJoh9nFSBZzVK6YmgaD7/KOcihFJWa9KTUFu7fD+FRN/vcTsjtM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765568299; c=relaxed/simple; bh=iX4bCRJMjNTc89J6Hb3IJZ8DlWuZIDZYYAn/N65O7DQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=bE/VU0690fHR3mjNIeJVQNkd83n5zdp4vwZSLP0FHOKkxlR28pTtdJsmPnRsZPcyT1dgsv/DCi8dw/ZsjtNcRT2kJdRtfSnZGT94Gw5LX+ohDji5/oliX66lnrq4UYXCyKyhKiWyfoF7iUyt37HeRGl45facnsg6NVCEBkKi6pA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=runbox.com; dkim=pass (2048-bit key) header.d=runbox.com header.i=@runbox.com header.b=Wpdx0hNl; arc=none smtp.client-ip=185.226.149.37 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=runbox.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=runbox.com header.i=@runbox.com header.b="Wpdx0hNl" Received: from mailtransmit03.runbox ([10.9.9.163] helo=aibo.runbox.com) by mailtransmit04.runbox.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1vU8xy-0087gq-OP; Fri, 12 Dec 2025 20:38:14 +0100 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=runbox.com; s=selector2; h=Content-Transfer-Encoding:MIME-Version:References:In-Reply-To :Message-Id:Date:Subject:Cc:To:From; bh=XGNNIc7IKcGdjBNdCWUpuNKT8BFgCw2QYiU5srDt8fQ=; b=Wpdx0hNlbtmydznicg6yGTxTE9 i+/7jgy7Yx8lPlzp4IottmUUrwCU1IO7VJPIaV+S9mAKgvv5A8OZ3sRJBJbMw5RvKwBcsmpFlxc+I gzPgX7iZw8yehHsqpHvCxT3blsWtG/ALesGkD3NxDxHZ7cGFURST/OO+qataDwXcEFCiS1JupodY9 +MJJYHxeE0swVBQr14URnBmXccDVKX1SEBxCHqXTuUhlNvgRbkAF8ct2aAHTv/o27QYRLND27O5qf E0srSaYNv34Z1fdRPpFGr6JG0/YHKacRjGcdcEooNVFmtY8cK7xF4PZt3+zWC5XbwGzqjSppGv8FK GvGn8jWQ==; Received: from [10.9.9.73] (helo=submission02.runbox) by mailtransmit03.runbox with esmtp (Exim 4.86_2) (envelope-from ) id 1vU8xy-0003Ac-6G; Fri, 12 Dec 2025 20:38:14 +0100 Received: by submission02.runbox with esmtpsa [Authenticated ID (1493616)] (TLS1.2:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.93) id 1vU8xn-0030pR-5E; Fri, 12 Dec 2025 20:38:03 +0100 From: david.laight.linux@gmail.com To: Yury Norov , Rasmus Villemoes , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, Geert Uytterhoeven , Alexandre Belloni , Jonathan Cameron , Crt Mori , Richard Genoud , Andy Shevchenko , Luo Jie , Peter Zijlstra , Jakub Kicinski , netdev@vger.kernel.org, "David S . Miller" , Mika Westerberg , Andreas Noever , Yehezkel Bernat , Nicolas Frattaroli Cc: David Laight Subject: [PATCH v2 14/16] bitfield: Add comment block for the host/fixed endian functions Date: Fri, 12 Dec 2025 19:37:19 +0000 Message-Id: <20251212193721.740055-15-david.laight.linux@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20251212193721.740055-1-david.laight.linux@gmail.com> References: <20251212193721.740055-1-david.laight.linux@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: David Laight Copied almost verbatim from the commit message that added the functions. Signed-off-by: David Laight --- include/linux/bitfield.h | 43 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h index 03206be4ab54..3bf82121a282 100644 --- a/include/linux/bitfield.h +++ b/include/linux/bitfield.h @@ -181,6 +181,49 @@ do { \ *_reg_p =3D (*_reg_p & ~_mask) | ((_val << __bf_shf(_mask)) & _mask); \ }) =20 +/* + * Primitives for manipulating bitfields both in host- and fixed-endian. + * + * * u32 le32_get_bits(__le32 val, u32 field) extracts the contents of the + * bitfield specified by @field in little-endian 32bit object @val and + * converts it to host-endian. + * + * * void le32p_replace_bits(__le32 *p, u32 v, u32 field) replaces + * the contents of the bitfield specified by @field in little-endian + * 32bit object pointed to by @p with the value of @v. New value is + * given in host-endian and stored as little-endian. + * + * * __le32 le32_replace_bits(__le32 old, u32 v, u32 field) is equivalent = to + * ({__le32 tmp =3D old; le32p_replace_bits(&tmp, v, field); tmp;}) + * In other words, instead of modifying an object in memory, it takes + * the initial value and returns the modified one. + * + * * __le32 le32_encode_bits(u32 v, u32 field) is equivalent to + * le32_replace_bits(0, v, field). In other words, it returns a little-= endian + * 32bit object with the bitfield specified by @field containing the + * value of @v and all bits outside that bitfield being zero. + * + * Such set of helpers is defined for each of little-, big- and host-endian + * types; e.g. u64_get_bits(val, field) will return the contents of the bi= tfield + * specified by @field in host-endian 64bit object @val, etc. Of course, = for + * host-endian no conversion is involved. + * + * Fields to access are specified as GENMASK() values - an N-bit field + * starting at bit #M is encoded as GENMASK(M + N - 1, M). Note that + * bit numbers refer to endianness of the object we are working with - + * e.g. GENMASK(11, 0) in __be16 refers to the second byte and the lower + * 4 bits of the first byte. In __le16 it would refer to the first byte + * and the lower 4 bits of the second byte, etc. + * + * Field specification must be a constant; __builtin_constant_p() doesn't + * have to be true for it, but compiler must be able to evaluate it at + * build time. If it cannot or if the value does not encode any bitfield, + * the build will fail. + * + * If the value being stored in a bitfield is a constant that does not fit + * into that bitfield, a warning will be generated at compile time. + */ + extern void __compiletime_error("value doesn't fit into mask") __field_overflow(void); extern void __compiletime_error("bad bitfield mask") --=20 2.39.5